What does discovery have anything to do with it? The article makes a different claim.

> What we now call “old-growth” forests are simply communities of trees that have been allowed to continue on undisturbed while most of the forest around them has been thinned or cut down entirely. In North America, even places that look thickly forested to us now are often full of relatively young trees, regrown on patches of land that were farms not so long ago.